Systems and methods for vehicle mapping and localization using synthetic aperture radar

Abstract

A system for generating a map is disclosed herein. The system may comprise a synthetic aperture radar (SAR) unit mountable to a terrestrial vehicle. The system may further comprise one or more computer processors operatively coupled to the SAR unit. The one or more computer processors may be individually or collectively programmed to: (i) while the terrestrial vehicle is in motion, use the SAR unit to (1) transmit a first set of signals to an environment external to the vehicle and (2) collect a second set of signals from the environment; and (ii) use at least the second set of signals to generate the map of the environment in memory.

What is claimed is: 
     
       1. A computer-implemented method for generating a map, the method being executed by an electronic processor and comprising:
 providing a pulse repetition frequency to a synthetic aperture radar (SAR) unit mounted on a terrestrial vehicle; 
 transmitting, via the SAR unit, a first set of signals at the pulse repetition frequency to an environment external to the terrestrial vehicle while the terrestrial vehicle is in motion; 
 receiving, via the SAR unit, a second set of signals from the environment; 
 receiving, from a vehicle position sensor, a third set of signals comprising position, orientation, and velocity measurements of the terrestrial vehicle while the terrestrial vehicle is in motion; 
 generating a synchronized set of signals by temporally synchronizing the second set of signals and the third set of signals, and 
 generating the map of the environment based on the synchronized set of signals. 
 
     
     
       2. The method of  claim 1 , wherein the map comprises a local map having a plurality of features positioned relative to, and in a vicinity of the terrestrial vehicle. 
     
     
       3. The method of  claim 2 , further comprising:
 generating a plurality of local maps, wherein two or more of the plurality of local maps overlap with one another. 
 
     
     
       4. The method of  claim 3 , further comprising:
 generating a regional map that covers a plurality of regions within the environment by aligning the plurality of local maps to one another. 
 
     
     
       5. The method of  claim 4 , further comprising:
 determining a local motion of the terrestrial vehicle in the environment based on the aligned plurality of local maps. 
 
     
     
       6. The method of  claim 4 , further comprising:
 aligning one or more of the plurality of local maps with the regional map; and 
 determining a pose of the terrestrial vehicle based on the alignment. 
 
     
     
       7. The method of any one of  claims 2 through 4 , wherein the terrestrial vehicle comprises a controller comprising the electronic processor. 
     
     
       8. The method of  claim 4 , further comprising:
 generating the regional map by resolving local inconsistencies at loop closures and aligning to a reference set of global coordinates of the terrestrial vehicle. 
 
     
     
       9. The method of  claim 1 , wherein the second set of signals are generated upon the first set of signals interacting with at least one object in the environment. 
     
     
       10. The method of  claim 1 , wherein the SAR unit is mounted in a forward-facing direction, a rear-facing direction, a side-facing direction, or a squinted direction of the terrestrial vehicle. 
     
     
       11. The method of  claim 1 , wherein the vehicle position sensor comprises at least one member selected from the group consisting of an inertial measurement unit, a Global Navigation Satellite System (GNSS) receiver, a camera, a light detection and ranging (lidar) unit, a wheel encoder, and a radar. 
     
     
       12. The method of  claim 6 , wherein the pose comprises a position, orientation, and velocity of the terrestrial vehicle. 
     
     
       13. The method of  claim 12 , wherein the map comprises a SAR-based image comprising a plurality of features located within the environment. 
     
     
       14. The method of  claim 13 , wherein the map comprises a high definition (HD) map of the environment. 
     
     
       15. The method of  claim 13 , further comprising:
 updating the pose of the terrestrial vehicle based on a movement of the terrestrial vehicle through the environment. 
 
     
     
       16. The method of  claim 15 , further comprising:
 generating a plurality of SAR-based images or a plurality of SAR-based velocity estimates based on the movement of the terrestrial vehicle through the environment; and 
 updating the pose of the terrestrial vehicle based on the plurality of SAR-based images or the plurality of SAR-based velocity estimates. 
 
     
     
       17. The method of  claim 15 , further comprising:
 determining a refined tracklog of the terrestrial vehicle based on the updated pose. 
 
     
     
       18. The method of  claim 17 , further comprising:
 updating one or more previously generated SAR-based images or a localization result of the terrestrial vehicle based on the refined tracklog. 
 
     
     
       19. The method of  claim 17 , further comprising:
 generating tracklog estimates and SAR-based images based on the refined tracklog without modifying one or more previously generated SAR-based images or a localization result of the terrestrial vehicle. 
 
     
     
       20. The method of  claim 6 , further comprising:
 determining the pose of the terrestrial vehicle by comparing a set of features in a selected local map with a set of features in the regional map. 
 
     
     
       21. The method of  claim 1 , further comprising:
 determining a common clock; and 
 providing the common clock to the SAR unit and the vehicle position sensor, wherein the second set of signals and the third set of signals are temporally synchronized based on the common clock. 
 
     
     
       22. The method of  claim 1 , further comprising:
 receiving a clock signal from the SAR unit or the vehicle position sensor, wherein the second set of signals and the third set of signals are temporally synchronized based on the clock signal. 
 
     
     
       23. The method of  claim 22 , wherein the clock signal comprises a predetermined output rate. 
     
     
       24. The method of  claim 22 , wherein the clock signal is determined based on a sampling frequency of the SAR unit. 
     
     
       25. The method of  claim 1 , further comprising:
 determining a phase shift measurement based on a difference in phase between the first set of signals and the second set of signals, wherein the second set of signals and the third set of signals are temporally synchronized based on the phase shift measurement. 
 
     
     
       26. The method of  claim 1 , further comprising:
 determining the pulse repetition frequency based on a maximum velocity of the terrestrial vehicle and a value defined according to a center frequency of successive radar pulses. 
 
     
     
       27. The method of  claim 1 , further comprising:
 determining the pulse repetition frequency based on an inverse of a time duration for the terrestrial vehicle to travel a set fraction of a wavelength of radar pulses transmitted by the SAR unit. 
 
     
     
       28. A system for generating a map, comprising:
 a first synthetic aperture radar (SAR) unit mountable to a terrestrial vehicle; 
 a second SAR unit mountable to the terrestrial vehicle; and 
 a computer processor operatively coupled to the first SAR unit and the second SAR unit, wherein the computer processor is programmed to:
 provide a lower and upper cutoff frequency to the first SAR unit and the second SAR unit; 
 transmit, via the first SAR unit and the second SAR unit, a first set of signals based on the lower and upper cutoff frequency to an environment external to the terrestrial vehicle; 
 receive, via the first SAR unit, a second set of signals from the environment; 
 receive, via the second SAR unit, a third set of signals from the environment; 
 generate a synchronized set of signals by temporally synchronizing the second set of signals and the third set of signals; and 
 generate the map of the environment based on the synchronized set of signals. 
 
 
     
     
       29. The system of  claim 28 , further comprising the terrestrial vehicle, wherein the first SAR unit and the second SAR unit are mounted on the terrestrial vehicle. 
     
     
       30. The system of  claim 28 , further comprising:
 a vehicle position sensor mountable to the terrestrial vehicle; 
 wherein the computer processor is operatively coupled to the vehicle position sensor and further configured to:
 receive, from the vehicle position sensor, a fourth set of signals comprising position, orientation, and velocity measurements of the terrestrial vehicle; and 
 generate the synchronized set of signals by temporally synchronizing the second set of signals, the third set of signals, and the fourth set of signals. 
 
 
     
     
       31. The system of  claim 30 , wherein the vehicle position sensor comprises at least one member selected from the group consisting of an inertial measurement unit, a Global Navigation Satellite System (GNSS) receiver, a camera, a light detection and ranging (lidar) unit, a wheel encoder, and a radar. 
     
     
       32. The system of  claim 30 , wherein the computer processor is further configured to:
 determine a common clock; and 
 provide the common clock to the first SAR unit, the second SAR unit, and the vehicle position sensor, wherein the second set of signals, the third set of signals, and the fourth set of signals are temporally synchronized based on the common clock. 
 
     
     
       33. The system of  claim 28 , wherein the computer processor is further programmed to:
 determine the lower and upper cutoff frequency based on a maximum velocity of the terrestrial vehicle. 
 
     
     
       34. The system of  claim 28 , wherein the computer processor is further programmed to:
 determine the lower and upper cutoff frequency based on an inverse of a time duration for the terrestrial vehicle to travel a set fraction of a wavelength of radar pulses transmitted by the first SAR unit or the second SAR unit.